The invention relates to a disc brake of hydraulic self-energizing design with a force transmission unit.
A disc brake with an electromotive actuator of self-energizing design and with a brake-internal hydraulic arrangement is described in the Applicant's application WO 2007/045430 A1.
Such a disc brake consists of a considerable number of parts and is associated with corresponding costs.
It is the object of the present invention to improve a generic disc brake.
It is thereby possible to realize a disc brake which permits the construction of a compact disc brake with a smaller number of parts than in the prior art.
According to the invention, the disc brake is equipped with at least one force transmission unit which has a diverting lever and a shoulder element attached thereto. The diverting lever and the shoulder element have rolling surfaces which are in contact with respective corresponding rolling surfaces of a brake-application element of the at least one brake-application cylinder and of a support device of the brake pad. The diverting lever has a thrust portion with a rolling surface which is operatively connected to the at least one tangential force absorption cylinder.
Therefore, in a simple manner, a disc brake having a force transmission unit is provided which has an element for transmitting brake-application forces and an element for transmitting tangential forces, wherein as a result of the design of rolling surfaces which are in contact, friction losses are reduced and robustness is increased.
A self-energizing disc brake includes the following: a brake-internal hydraulic arrangement with a reservoir circuit and an expansion vessel; a brake-application device having at least one brake-application cylinder for the brake-application movement of at least one brake pad in the direction of a brake disc; at least one force transmission unit which supports the at least one brake pad on the brake-application device at a wedge angle; at least one tangential force absorption cylinder for wedge angle switching, which tangential force absorption cylinder is operatively connected to the at least one force transmission unit; an electromotive actuator which acts on the brake-application device via the hydraulic arrangement; and a control unit which is provided for controlling the wedge angle switching between the tangential force absorption cylinder and the electromotive actuator. At least one force transmission unit has a diverting lever and a shoulder element attached thereto, wherein the diverting lever and the shoulder element have rolling surfaces which are in contact with respective corresponding rolling surfaces of a brake-application element of the at least one brake-application cylinder and of a support device of the brake pad, and further wherein the diverting lever has a pressure portion with a rolling surface which is operatively connected to the at least one tangential force absorption cylinder.
In the case of two or more brake-application cylinders, a distributor cylinder for pressure boosting may be arranged in series between the electromotive actuator and the brake-application device. This also offers the advantage that it compensates oblique wear of the brake pads and reduces a pressure level between the tangential absorption cylinder and the distributor cylinder.
A particularly large reduction of friction in the interacting functional units is attained in that the diverting lever has a tooth portion which is provided for interacting with a tooth counterpart of the brake-application element. The tooth contour is selected such that the toothing behaves, on both sides, in the manner of two gearwheels running into one another. This means that the same low-friction processes as those encountered during the rolling of tooth flanks on one another arise.
The tooth counterpart may be a separate component for attaching to the at least one brake-application element. In this way, a machining process for creating the toothing can be performed separately on a corresponding machine.
The support device may also be formed with a portion produced for example as a tooth. Between the support device and a force transfer portion of the lever and a shoulder connected thereto there may be arranged a roller element which rolls on the surface.
It is preferable for the shoulder of the diverting lever to have a planar surface and for the support portion of the support device, in particular in the form of a tooth, to have a curved surface. Combinations are however also possible: the shoulder of the diverting lever may have a planar or curved surface, wherein the support portion of the support device likewise has a curved or planar surface.
The curvatures of the surfaces may be calculated so as to correspond exactly harmonically to rolling movements on the support device.
A pitch point, at which sliding-free rolling takes place, between the at least one force transmission unit, the at least one brake-application cylinder and the support device of the brake pad may be selected so as to be situated at one third of a maximum tangential deflection of the brake pad. There is therefore no relative displacement, for example between tooth and counterpart contour, at one third of the maximum deflection. This is advantageous because, in the frequency distribution of brake-application movements, the greatest number of brake actuations takes place with one third of the maximum deflection, that is to say with one third of a maximum brake-application force, whereas a maximum brake-application force is encountered relatively rarely.
Such a pitch point may self-evidently also be provided in the embodiment in which the diverting lever has the tooth portion which is provided for interacting with the tooth counterpart of the brake-application element.
The shoulder element may be connected to the diverting lever by way of a resilient plate-spring screw connection. It is ensured in this way that, even in the case of broadened production tolerances, no slippage with increased friction arises during a rolling process.
The shoulder element may have portions for brake-application force transmission for interacting with the at least one brake-application cylinder and the support device of the brake pad. The portions may be provided with rolling surfaces, whereby friction is reduced. Furthermore, a splitting-up of forces is made possible, wherein the shoulder element preferably transmits brake-application forces and the diverting lever transmits tangential forces.
In one embodiment, the shoulder element may have a narrowed portion for generating a small degree of elasticity. Rolling without slipping is permitted in this way.
The shoulder element has freedom of movement relative to the diverting lever, which advantageously simultaneously permits a slippage-free rolling movement of the vertical brake-application force by way of the shoulder element and of the horizontal braking force by way of the roller element.
The disc brake may furthermore include a readjustment device for readjustment of brake pad wear, wherein the readjustment device has an adjustable screw spindle, which is operatively connected to the brake-application device for the purpose of generating a follow-up movement of the at least one brake pad and can be coupled to the electromotive actuator in order to be driven, and a readjustment piston, which can be hydraulically adjusted in the tangential force absorption cylinder during a follow-up movement of the at least one brake pad.
In a further embodiment, it is provided that the control unit is connected to the reservoir circuit and to an intermediate circuit, wherein the electromotive actuator is connected to the reservoir circuit by way of a suction valve and can be connected to the intermediate circuit by way of a switching valve when the latter is in a first position.
It may be the case here that, in the first position of the switching valve, a change in a brake application movement can be performed only through adjustment of the electromotive actuator. The control unit may be designed, in interaction with a stepped absorption piston of the tangential force absorption cylinder, to select an effective wedge angle closest to a present friction coefficient of the brake pad.
It is particularly advantageous here that the brake force can be increased or reduced only through an adjustment of a control disc, which may for example be in the form of a perforated disc. Here, the control disc can selectively connect pressure chambers, which are connected to the stepped absorption piston of the tangential force absorption cylinder, to the reservoir circuit and/or to the intermediate circuit.
A particular graduation of wedge angles is made possible in that the selective connection of the pressure chambers to the reservoir circuit and/or to the intermediate circuit can be switched, based on the operating principle of binary coding, in seven stages with increasing effective piston surface area of the stepped absorption piston.
The electromotive actuator can be connected to the hydraulic control drive of the control unit, in order to switch the selective connections for the purpose of selecting a shallower or steeper wedge angle, by use of the switching valve when the latter is in a second position. Here, the electromotive actuator performs an additional function and saves space. During switching, it is, for example, possible for a pump suction line of the actuator to be blocked with a pump pressure line. A change in a brake-application position is then not possible during the short switching process.
It may advantageously also be provided that, to save power during relatively long, uniform braking operations, despite a pressure difference existing across the electromotive actuator, the electric motor thereof can be switched into a deenergized state by virtue of the switching valve being switched from the first position into the second position.
In order that a presently selected brake-application position remains unchanged, the control unit may have further switching positions, such that between each of the selective connections or each of the possible switchable wedge angles, there exists a blocking position in which the pressure chambers and connections to the reservoir circuit and/or to the intermediate circuit are shut off.
The electromotive drive is operatively connected only to the control drive of the control unit for the entire duration of a braking operation.
In a further embodiment, it may be provided that, during a period in which a brake-application position is constant, the perforated or control disc is in a blocking position situated between a wedge angle more supercritical in relation to the present wedge angle and a wedge angle more subcritical, and that in this position, the electromotive actuator is deenergized.
In the event of a demand for a slightly more intense brake application by way of the electromotive actuator and the control drive, the perforated or control disc may be adjustable such that the perforated or control disc is adjusted, in the manner of operation of a proportional valve, from the blocking position slowly in the direction of the position of a supercritical wedge angle. In the event of a contrary demand, the perforated or control disc is, in a similar manner, adjusted from the blocking position slowly in the direction of the position of a subcritical wedge angle.
Furthermore, for the purpose of a fast release of the brake, for example in the event of a fault or in the event of a failure of the supply voltage of the brake, the brake-internal hydraulic arrangement may have a release valve, which generates a through-connection in the deenergized state, for an immediate and reliable release of the brake.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.